1. Technical Field
The present invention relates to a deposition apparatus and method for depositing a film.
2. Related Art
In semiconductor devices of recent years, a delay in signal propagation through an interconnect restricts an operating speed of electronic elements. A delay constant in signal propagation through an interconnect is represented by a product of an interconnect resistance and an interconnect capacitance. Therefore, in order to achieve faster operation of elements, a low dielectric constant material having lower dielectric constant than a conventional silicon dioxide film (SiO2) is employed for an interlayer insulating film, and copper (Cu) having lower resistivity is employed for an interconnect.
A multiple-layered interconnect employing copper as an interconnect material is formed by a damascene process. In typical damascene process, a concave portion such as an interconnect trench or a via hole is formed in an interlayer insulating film, and then a barrier metal film is deposited in the concave portion, and the concave portion is further plugged with a copper film, and thereafter, portions of the copper film and the barrier metal film deposited outside of the concave portion are removed by a chemical mechanical polishing (CMP) process to obtain a copper interconnect or a copper via.
In such copper interconnect or copper via, a barrier metal film is composed of, for example, a titanium nitride (TiN) film. A resistivity of such barrier metal film is higher than copper by several-folds to several tens-folds. Therefore, as the interconnect dimension is decreased, the film thickness of the barrier metal film should also be reduced, and otherwise, a contribution of the barrier metal in the interconnect is increased, leading to unwanted increase in the interconnect resistance. Consequently, a reduction of the film thickness of the barrier metal film is particularly critical in the post-45 nm technology node. Meanwhile, the barrier metal film is required to have a certain level of film thickness, in order to maintain a barrier-ability against a diffusion of copper and/or an adhesiveness between the copper film and the interlayer insulating film. To meet these demands, higher step coverage and higher deposition uniformity across the wafer surface are required in the process for depositing the barrier metal film. Therefore, developments in an atomic layer deposition (ALD) process, which can achieve higher step coverage and higher deposition uniformity across the wafer surface, is proceeded.
Japanese Laid-open patent publication No. 2005-229,129 discloses an ALD process employing a plasma (plasma enhanced ALD, PEALD). In such process, a plasma-processing is carried out in every cycle of supplying a reactive gas or after several cycles of supplying a reactive gas are repeated to form a titanium nitride (TiN) film or the like.
Japanese Laid-open patent publication No. 2005-203,569 discloses a method for manufacturing a semiconductor device includes: a first operation for forming a first barrier metal thin film on a substrate by employing a first gas and a second gas for inducing a reduction of the first gas; and a second operation for forming a second barrier metal thin film on the first barrier metal thin film formed by the first operation for forming the first barrier metal thin film by employing a third gas and a fourth gas for inducing a reduction of the third gas without exposing the substrate in an atmospheric air. A procedure for exposing the substrate to plasma atmosphere of the fourth gas in the second operation for forming the barrier metal thin film is disclosed.
Japanese domestic re-publication of PCT international application No. 2005-523,580 discloses a remote plasma ALD apparatus, which comprise: a reaction chamber; an exhaust line for exhausting a gas from the reaction chamber; a first reactive gas supplying unit for selectively supplying the first reactive gas to the reaction chamber or the exhaust line; a first reactive gas transfer line that connects the reaction chamber with the first reactive gas supplying unit; a first bypass line that connects the exhaust line with the first reactive gas supplying unit; a radical supplying unit for generating radical and for selectively supplying such radical to the reaction chamber or the exhaust line; a radical transfer line that connects the reaction chamber with the radical supplying unit; a second bypass line that connects the exhaust line with the radical supplying unit; and main purge gas supplying unit for supplying main purge gas to the first reactive gas transfer line and/or a radical transfer line.
Japanese Laid-open patent publication No. 2003-41,367 discloses a substrate processing apparatus, in which, when a combination of a gas with a need for being excited and a gas without a need for being excited is flown in a common supplying system disposed in a downstream of an excitation unit, the gas without a need for being excited can be appropriately supplied into a reaction chamber in a condition of being not excited. Japanese Laid-open patent publication No. H10-284,487 (1998) discloses a process for depositing a Si—O—F insulating layer on a substrate within a chemical vapor deposition (CVD) processing chamber. A system dedicated for implementing such process comprises: a vacuum chamber; a gas distribution system, which is capable of introducing a gaseous mixture containing dissociated silicon tetrafluoride (SiF4) radical and an oxygen-containing gas into the vacuum chamber, where an Si—F—O film is deposited on a wafer by a thermal reaction of the introduced process gas; and an excitation chamber for dissociating SiF4 gas to create SiF4 radical, disposed remote from the vacuum chamber and connected to the gas distribution system.
In the mean time, in deposition apparatus such as ALD apparatus, a flow rate of a source gas supplied in a reaction chamber is controlled by a mass flow controller (MFC). On the other hand, an ALD deposition generally requires frequently supplying a source material with shorter intervals than the opening and closing operation by the MFC for providing an improved throughput. Consequently, a valve is provided between the MFC and the reaction chamber, and an operation for controlling a supply of a source gas is performed by opening and closing the valve while the MFC is kept open in the deposition process (see Japanese domestic re-publication of PCT international application No. 2005-523,580 and Japanese Laid-open patent publication No. 2003-41,367).
However, such operation causes an increased pressure between the MFC and the valve, as compared with a pressure in supplying the source gas, while the valve is closed so that the source gas is not supplied in the reaction chamber. In consequence of such phenomenon, the pressure in the reaction chamber becomes higher right after the valve is opened, leading to larger flow rate of the supplied source gas, and then the flow rate of the supplied source gas is decreased. Such change in the rate of the supplied source material adversely affects the deposition characteristics, and causes deterioration in the deposition uniformity across the wafer surface. In particular, in the PEALD process as illustrated in Japanese Laid-open patent publication No. 2005-229,129, Japanese Laid-open patent publication No. 2005-203,569 and Japanese Laid-open patent publication No. 2003-41,367, the rate of the supplied gas employed for a plasma-processing is influential in purity of the deposited film. Therefore, a flow rate of the gas for a plasma-processing is often selected to be larger than flow rates of other gases. Consequently, a fluctuation in the pressure of the gas for a plasma-processing is more critical issue in the PEALD process, as compared with ALD processes without plasma. Nevertheless, a consideration for such pressure fluctuation is not included in the technologies disclosed in Japanese Laid-open patent publication No. 2005-229,129, Japanese Laid-open patent publication No. 2005-203,569 and Japanese Laid-open patent publication No. 2003-41,367.
In addition, another issue related to the ALD process is that an use of multiple types of gases inevitably causes a complicated duct configuration. In the technology described in Japanese Laid-open patent publication No. H10-284,487, the duct system is to be simplified by utilizing a gas mixing chamber to constitute a duct for connecting from the gas mixing chamber to the reaction chamber with a single duct. However, gases are simultaneously supplied in such configuration, and therefore there is a problem that the ALD deposition process cannot be performed by such configuration. In addition, the above-described issues of a pressure fluctuation can not be avoided even if such technology is employed.
The configuration as disclosed in Japanese domestic re-publication of PCT international application No. 2005-523,580 can allow a gas flowing into a reaction chamber or an exhaust line on a steady basis. Having this configuration, a change in the pressure between the MFC and the valve, which is the above-mentioned problem, can be reduced. However, such process causes a discharge of the unconsumed source material, leading to an increased consumption of the source material. Further, when the configuration as described in Japanese domestic re-publication of PCT international application No. 2005-523,580, in which two types of reactive source gases are simultaneously and directly exhausted via the exhaust line without passing through the deposition chamber, is employed, it is possible that the source materials are reacted within the exhaust line and the line is clogged. If such problem is to be avoided, another problem of having a complicated apparatus configuration, which is caused by having separated ducts and/or arrangements for avoiding the difficulties, is caused.